Take-off of Unmanned Aerial Vehicles (UAV's) is in some cases performed by using a winch towing a dolly on which the aircraft is mounted and carried until its speed is high enough to rotate and take-off. This method is used in order to save energy for the flight and/or to keep a clean and lighter configuration of the aircraft, avoiding the use of a heavy and bulky landing gear. The use of this method usually involves a winch operator, who must coordinate with the manual pilot in order to start the system just prior to the take-off and to stop it once the plane has lifted off from the dolly. A system like the one previously described is disclosed in European Patent application EP 14382030.6.
However, the system disclosed in the mentioned patent application involves, as has been said, a dedicated person who is in charge of managing the winch and coordinating with the aircraft's pilot (be it a manual pilot, an autopilot, or a Ground Control Station (GCS)) in order to perform a safe take-off for the aircraft. Apart from the fact of this task being quite cumbersome for a human winch operator, there are several safety aspects that must be taken into consideration when analyzing the performance of a system like the one mentioned above.
First, one should notice the possible misunderstandings that may occur among the aircraft's pilot and the winch operator during take-off maneuvers. Second, and more importantly, any emergencies or malfunctions arising during a take-off maneuver have to be rapidly recognized and communicated from the aircraft's pilot to the winch operator, in order for the winch operator to stop the winch so that it does not continue towing the dolly, thus aborting the take-off in time. The response time in these events is critical, and it is important that it be as short as possible, preferably not exceeding a few seconds.
Other safety aspects that should be taken into consideration when managing a system like the one previously described, is the necessity of checking the winch battery level, to ensure, prior to the aircraft's take-off, that the battery level is high enough to carry on an entire take-off cycle, which involves deploying and further rolling up of the towline.
Measuring the deployed towline is another task which is crucial for a safe take-off, because this allows knowing the runway available for the dolly, in order for the aircraft to have sufficient time to gain velocity and take off. This task must also be carried out by the winch operator in the system described above.
In the cases where aborting the take-off of the aircraft is necessary, one should bear in mind that the conditions surrounding the aircraft might be unexpectedly worse than usual (such as wind gusts or ambient noise that may influence communication between the pilot and the winch operator). This implies the criticality of a prompt response taken by the aircraft, and the necessity of good communication channels among the pilot and the winch operator. However, a rapid and timely response may sometimes be difficult to achieve, which can lead to a failed take-off and damage to the aircraft.